Tasks in the Spatial Analysis service run asynchronously, meaning that you submit a request (or job) and then poll the service for status. When you submit a request, the Spatial Analysis service returns a unique job ID for the transaction. You can use the job ID to periodically check the status of the job and messages.
Syntax:
http://<analysis url>/arcgis/rest/services/tasks/GPServer/<task name>/jobs/<jobId>The job will start with a status of esri. When the job has successfully completed, the job status will change to esri and the resultsresource will be populated. You can append the paramvalue from the resultsresource to the request with the job ID to retrieve the results of the task.
jobStatus values
The job property can have the following values:
esriJ o b Submitted esriJ o b Waiting esriJ o b Executing esriJ o b Succeeded esriJ o b Failed esriJ o b Timed Out esriJ o b Cancelling esriJ o b Cancelled